A micro magnetic field sensor is an element widely applied to, for example, smart phones, wearable devices and Internet of Things (IOT) devices. The micro magnetic field sensor may also be applied to other fields of engineering, science, and industry. For providing a function of magnetic measurement on a modern application, the micro magnetic field sensor has to be highly integrated, have low power consumption, and provide correct magnetic force/magnetic field measurement.
In various micro magnetic field sensors, the magnetic field sensor operating on the principle of the Lorentz forces is practical. The reason is that this kind of micro magnetic field sensor can be manufactured in a standard CMOS process. Most new micro magnetic field sensor structures operate using the principle of the Lorentz forces.
A magnetic field sensor using the Lorentz forces substantially comprises a mass block which is suspended on a structure or a substrate via a spring. When a certain current is applied to the mass block, the current and magnetic forces existing in the earth magnetic field or generated by other magnetic objects generate the Lorentz forces, that move the mass block in a direction perpendicular to the current direction and the magnetic force direction. An electrode for detection forms generally in a comb or finger shape which is staggered with a comb or finger shape formed by an edge of the mass block and maintained at intervals; and the space therebetween is equivalent to a capacitor. The electrode for detection can detect a change in capacitance due to a change in the relative position between the mass block and the electrode for detection caused by the movement of the mass block, and generate a detection signal. The detection signal is converted into a voltage form as an output signal. The generated output signal represents a displacement direction and a displacement amount of the mass block under the influence of the magnetic force, and a value of the magnetic force can be calculated on this basis.
Since most of the known micro magnetic field sensors are manufactured by an MEMS or CMOS process with a very small size, they can only provide single direction magnetism measurement. The industry has proposed several designs capable of measuring coplanar two-direction magnetism with a single magnetic field sensor. However, this kind of design cannot measure magnetism in a third direction perpendicular to this plane.
WO 2013159584 A1 discloses a micro-mechanical magnetic field sensor which can measure magnetism in two directions of X and Y simultaneously. However, this invention does not provide measurement of magnetism in a Z direction, i.e., perpendicular to the XY plane.
U.S. Pat. No. 8,637,943 B1 discloses a multi-axis integrated MEMS device which comprises 3 groups of magnetic field sensors to measure three-axis magnetism.
US 2012/0007597 A1 discloses a micro-mechanical magnetic field sensor structure which uses a group of X/Y-axis magnetic force detectors and a group of Z-axis magnetic force detectors so as to provide three-axis magnetic force measurement. The X/Y-axis magnetic force detectors and the Z-axis magnetic force detectors are detectors of different types.
U.S. Pat. No. 8,390,283 B2 provides a three-axis magnetic field sensor which uses three groups of Wheatstone bridges consisting of magneto-resistive sensors to provide a function of three-axis magnetic force detection.
At present, a novel structure of micro magnetic field sensor is needed in the industry to provide a function of three-axis magnetic force detection.
Meanwhile, a novel micro magnetic field sensor structure is also needed to provide a function of three-axis magnetic force detection using a single mass block.
Meanwhile, it is also necessary to provide a magnetic field sensor capable of integrating a three-axis magnetic force measurement function in a single mass block by taking the advantages of the standard CMOS process.